The present invention relates to an access control device for a disk-based recording and reproducing system, and particularly to an access control device which is so designed as to provide a high precision rough access to a target position by preparing in advance reference velocity information corresponding to various access target positions.
The access methods used in devices which record to and/or reproduce a disk-shaped recording medium in which information is recorded in concentric tracks or a spiral track divided into a specific number of recording units generally include rough and precision access controls. Rough access is used to position a recording/reproducing portion such as a head or a pick-up near a target track. Precision access following the rough access positions the recording/reproducing portion using servo control to the final target track and sector. Rough access is usually accomplished by means of a linear motor or similar drive, and by increasing the rough access precision, the time required for precision access can be shortened and the efficiency of the system can as a result be increased.
The first inventor, et al. of the present invention have previously proposed an access control device which was so designed as to accomplish a rough access with precision by making use of a relationship between physical positions and velocities of the recording/reproducing portion (Japanese Pat. application No. 62-113383, Laid-open No. 63-279478).
According to the access control device, a travel signal generator which may be a scale or similar device generates a travel signal corresponding to the movement of the recording/reproducing portion, and the travel signals are counted by a counter, so that an actual travel distance of the recording/reproducing portion is measured. Velocity control is carried out based on the actual travel distance and a target distance which must be traveled for rough access.
If the counter indicates zero, for example, as a predetermined counted value, when a predetermined time has elapsed after the rough access begins, the access control device judges that the recording/reproducing portion has traveled the target distance and informs a host controller device that the rough access has been normally finished. On the other hand, if the counter does not indicate zero at that time, the access control device considers that the rough access resulted in an error finish and informs the host controller device of the error.
However, if a recording and reproducing device provided with the above access control device is positioned with inclination, it is very possible for the counter not to be able to count correctly. In this case, even when the rough access is normally finished, the access device will wrongly inform the host controller device of an error finish of the rough access, when the host controller device must carry out an error routine which would not be required with a correct indication of the counter. This causes a time delay before servo control begins for driving an actuator carrying the recording/reproducing portion in the precision access stage.